7mm-08 would be fine choice. Just rebarrel, no need for magazine, follower, or feed rail changes.

A .270win might be what you are looking for. It's will be easy to rebarrel if you stay with the 06 sized cases. 7mm mag kicks .308 ass at very long range 800yds and beyond! The 7mm mag can be an effective target round to 1200yds.

I was orginal a 8x57 so any shell around that size will work I would go with 06. Unless you want something fast and light.

Well the .308 barrel on my M98 has finally come to the end of it's accurate life. After 60 years (not all from me!) of service I am not complaining. I have no problem to get another .308win barrel. I have dies, brass, bullets for it and all in all happy with the cartridge.

But while I have the chance now what other cartridges should I look at? Perhaps 30-06 or 7mm Rem Mag or even 8mm Mauser? Will my action support the longer cases?

How accurate are these other cartridges compared to the 308? I know the big 7 shoots flatter but what about grouping over long distances? Any other suggestions?